The present invention relates to load cells and particularly to load cells that generate signals indicative of loads applied to the load cells. More particularly the present invention relates to load cell isolation in load cell systems.
It is well known to use load cells to sense loads. Conventional load cells typically include a block and one or more strain gages mounted to the block. Deflection of the block due to an applied load changes the shape of the strain gages resulting in a change in the resistance of the strain gages. Generally, a known input voltage is applied to the strain gages and an output signal from the strain gages varies as the resistance of the strain gages vary to provide a signal indicative of the load applied to the load cell. Load cells are sometimes used in hospital beds as part of a weigh system that senses, for example, the weight of a patient supported by the bed. It is desirable, of course, for weigh systems to provide accurate weight readings and therefore, it is desirable to minimize sources of error that may contribute to inaccurate output signals from the load cells.
According to an illustrated embodiment of the present invention, a load cell apparatus includes a cell block adapted to couple to a first structure, a mount adapted to couple to a second structure, and a stud extending from the cell block. The mount is made of a first material and is formed to include a bore. The load cell apparatus further includes a liner that is positioned to lie in the bore and that engages the stud. The liner is made of a second material that is more lubrous than the first material.
In one embodiment, the stud extending from the cell block includes a cylindrical portion and the liner is formed to include a cylindrical cavity that receives the cylindrical portion of the stud. In addition, the bore of the mount is generally square-shaped and the outer surface of the liner is square-shaped. In this embodiment, the liner press fits into the bore of the mount. The liner may include portions that protrude from the outer surface thereof to enhance the press fit of the liner in the bore of the mount.
In another embodiment, the stud extending from the cell block includes a cylindrical portion and the liner comprises a pad of material positioned to lie in the bore underneath the cylindrical portion of the stud. In yet another embodiment, the stud extending from the cell block includes a spherical portion and the liner comprises a pad of material positioned to lie in the bore underneath the spherical portion of the stud.
In a further embodiment, the stud extending from the cell block includes a cylindrical portion and the liner coats the stud. In this embodiment, the coated stud extends into the bore and engages the mount. In yet another embodiment, the stud extending from the cell block includes a spherical portion and the liner is formed as an O-ring coupled to the spherical portion.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of illustrated embodiments exemplifying the best mode of carrying out the invention as presently perceived.